The present disclosure relates to an antenna module and a wireless communication apparatus which are usable to transmit and receive radio signals in wireless networks, local area networks, mobile communications, GPS receivers, and the like in conformity with the specifications of IEEE802.15.4, IEEE802.11 and the like.
Wireless communications technologies are employed in various fields, such as wireless networks, local area networks, mobile communications, and GPS receivers in conformity with the specifications of IEEE802.15.4, IEEE802.11 and the like. In recent years, wireless communication devices have been gradually replacing infrared communication devices in the field of remote control of various consumer electronics products.
An antenna module is necessary for a wireless communication device to radiate radio waves of predetermined frequencies into space. A half-wave dipole antenna and a λ/4 monopole antenna are used as basic antennas. The half-wave dipole antenna has a length equal to a half of the wavelength λ in use, and a cycle of a standing wave exists thereon. The λ/4 monopole antenna has characteristics equivalent to those of dipole antennas when image currents on an infinite conducting plate are taken into account.
An inverted-F antenna, which is also used, is a monopole antenna with an end portion folded to have a low profile and with a short-circuiting portion formed near the feeding point to provide impedance matching. To further reduce the height of the antenna and to provide impedance matching, the folded horizontal portion facing the ground plane is made to be planar.
An antenna usually has a principal polarization plane, and has low gains for polarized waves that are orthogonal to the principal polarization plane. For example, a dipole antenna installed vertically has a high gain of vertically-polarized wave while a low gain of the horizontally-polarized wave. In addition, a monopole antenna has radiation pattern only above the infinite ground plane, and have no directional pattern below the ground. The inverted-F antenna has a directional pattern similar to that of the monopole antenna. The inverted-F antenna has a low gain on the opposite side of a board where the antenna is provided on the other side of the board, and has a low gain of the horizontally-polarized wave parallel to the board.
Ordinarily, in a wireless communication apparatus, an antenna is positioned to have a gain in a direction suitable for use situation. Regarding the usages of such apparatuses, however, in some cases, it is difficult to place the apparatus in a suitable direction in which radio signals are transmitted or received. In the case of a wireless-communication-type remote control system, for example, users are expected to hold a remote controller in various ways and transmit remote control signals in various directions to an antenna installed in an apparatus such as a TV set to be controlled by the remote controller. In flat-screen televisions, which have recently become popular in the market, the antenna is generally installed in a frame portion in the front surface of the television set. In some cases, the frame portion has some places allowing only vertically-polarized waves to pass therethrough and other some places allowing only horizontally-polarized waves to pass therethrough. It is preferable that the antennas be capable of transmitting or receiving both the vertically-polarized waves and horizontally-polarized waves.
In this regard, an inverted-F metal-plate antenna has been proposed which includes short-circuiting conductor plates provided to extend from several portions of periphery of the radiating conductor plate. The short-circuiting conductor plates exert plural resonant modes with different resonant lengths when electric power is applied (see, for example, Japanese Unexamined Patent Application Publication No. 2004-312166). The antenna of this type with the plural resonant modes can cover a wider band, but the effect thereof on the transmitting and receiving of the polarized waves is not disclosed.
For another example, a planar inverted-F antenna has been proposed which includes a printed board with a ground pattern which is entirely formed thereon except a region below the rectangular conductive plate of the planer inverted-F antenna (see, for example, Japanese Unexamined Patent Application Publication No. 2003-92510). Consequently, the antenna has a nearly omnidirectional antenna pattern that provides a high gain in the horizontal direction, i.e., the direction parallel to the printed circuit board, and provides a gain, which is not reduced to small, on the back side of the printed board.
For another example, an antenna unit has been proposed which includes patch antenna elements 11 and 12 provided on opposite surfaces of a board, a GND layer 13 provided between the elements, and an RF circuit 16 built inside of a hollow portion of the board (see Japanese Unexamined Patent Application Publication No. 2001-339239, paragraphs [0010] to [0020], and FIG. 1). In the antenna unit, the antenna element 11 and 12 are arranged in a peripheral of the board and the RF circuit 16 is arranged inside the board to reduce mutual influence between the antenna elements and the RF circuit 16 as much as possible.
The antenna unit is manufactured with an intention that the unit has an omnidirectional circularly polarized pattern and has an RF circuit inside a hollow portion of the body. The antenna unit has a structure in which both the module with the antenna and the RF circuit provided at the central portion inside the body are completely shielded. Hence, the antenna unit is very thick and difficult to manufacture.
A circularly polarized patch antenna apparatus has been proposed that includes circularly polarized patch antenna elements 2a, 2b, and 2c provided on outer surfaces of a cubic structure and a GND conductor body 7 and an RF circuit 92 provided on inner surfaces of the cubic structure (see Japanese Unexamined Patent Application Publication No. 2001-332929, paragraphs [0047] to [0055], and FIG. 8).
The circularly polarized patch antenna apparatus is manufactured with an intention that the apparatus has an omnidirectional circularly polarized pattern and has an RF circuit inside the cubic structure. The RF circuit 92 of the circularly polarized patch antenna apparatus is completely shielded with the GND conductor body 7. As a result, the RF circuit 92 is shielded to a very high degree, however, the downsizing and manufacturing of the antenna unit is difficult.